Varactor with hyper-abrupt junction region including a superlattice

ABSTRACT

A semiconductor device may include a substrate and a hyper-abrupt junction region carried by the substrate. The hyper-abrupt junction region may include a first semiconductor layer having a first conductivity type, a superlattice layer on the first semiconductor layer, and a second semiconductor layer on the superlattice layer and having a second conductivity type different than the first conductivity type. The superlattice may include stacked groups of layers, with each group of layers including stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The semiconductor device may further include a first contact coupled to the hyper-abrupt junction region, and a second contact coupled to the substrate to define a varactor.

TECHNICAL FIELD

The present disclosure generally relates to semiconductor devices and,more particularly, to semiconductor devices including hyper-abruptjunctions and related methods.

BACKGROUND

Structures and techniques have been proposed to enhance the performanceof semiconductor devices, such as by enhancing the mobility of thecharge carriers. For example, U.S. Patent Application No. 2003/0057416to Currie et al. discloses strained material layers of silicon,silicon-germanium, and relaxed silicon and also including impurity-freezones that would otherwise cause performance degradation. The resultingbiaxial strain in the upper silicon layer alters the carrier mobilitiesenabling higher speed and/or lower power devices. Published U.S. PatentApplication No. 2003/0034529 to Fitzgerald et al. discloses a CMOSinverter also based upon similar strained silicon technology.

U.S. Pat. No. 6,472,685 B2 to Takagi discloses a semiconductor deviceincluding a silicon and carbon layer sandwiched between silicon layersso that the conduction band and valence band of the second silicon layerreceive a tensile strain. Electrons having a smaller effective mass, andwhich have been induced by an electric field applied to the gateelectrode, are confined in the second silicon layer, thus, an re-channelMOSFET is asserted to have a higher mobility.

U.S. Pat. No. 4,937,204 to Ishibashi et al. discloses a superlattice inwhich a plurality of layers, less than eight monolayers, and containinga fractional or binary or a binary compound semiconductor layer, arealternately and epitaxially grown. The direction of main current flow isperpendicular to the layers of the superlattice.

U.S. Pat. No. 5,357,119 to Wang et al. discloses a Si—Ge short periodsuperlattice with higher mobility achieved by reducing alloy scatteringin the superlattice. Along these lines, U.S. Pat. No. 5,683,934 toCandelaria discloses an enhanced mobility MOSFET including a channellayer comprising an alloy of silicon and a second materialsubstitutionally present in the silicon lattice at a percentage thatplaces the channel layer under tensile stress.

U.S. Pat. No. 5,216,262 to Tsu discloses a quantum well structurecomprising two barrier regions and a thin epitaxially grownsemiconductor layer sandwiched between the barriers. Each barrier regionconsists of alternate layers of SiO2/Si with a thickness generally in arange of two to six monolayers. A much thicker section of silicon issandwiched between the barriers.

An article entitled “Phenomena in silicon nanostructure devices” also toTsu and published online Sep. 6, 2000 by Applied Physics and MaterialsScience & Processing, pp. 391-402 discloses a semiconductor-atomicsuperlattice (SAS) of silicon and oxygen. The Si/O superlattice isdisclosed as useful in a silicon quantum and light-emitting devices. Inparticular, a green electroluminescence diode structure was constructedand tested. Current flow in the diode structure is vertical, that is,perpendicular to the layers of the SAS. The disclosed SAS may includesemiconductor layers separated by adsorbed species such as oxygen atoms,and CO molecules. The silicon growth beyond the adsorbed monolayer ofoxygen is described as epitaxial with a fairly low defect density. OneSAS structure included a 1.1 nm thick silicon portion that is abouteight atomic layers of silicon, and another structure had twice thisthickness of silicon. An article to Luo et al. entitled “Chemical Designof Direct-Gap Light-Emitting Silicon” published in Physical ReviewLetters, Vol. 89, No. 7 (Aug. 12, 2002) further discusses the lightemitting SAS structures of Tsu.

U.S. Pat. No. 7,105,895 to Wang et al. discloses a barrier buildingblock of thin silicon and oxygen, carbon, nitrogen, phosphorous,antimony, arsenic or hydrogen to thereby reduce current flowingvertically through the lattice more than four orders of magnitude. Theinsulating layer/barrier layer allows for low defect epitaxial siliconto be deposited next to the insulating layer.

Published Great Britain Patent Application 2,347,520 to Mears et al.discloses that principles of Aperiodic Photonic Band-Gap (APBG)structures may be adapted for electronic bandgap engineering. Inparticular, the application discloses that material parameters, forexample, the location of band minima, effective mass, etc., can betailored to yield new aperiodic materials with desirable band-structurecharacteristics. Other parameters, such as electrical conductivity,thermal conductivity and dielectric permittivity or magneticpermeability are disclosed as also possible to be designed into thematerial.

Furthermore, U.S. Pat. No. 6,376,337 to Wang et al. discloses a methodfor producing an insulating or barrier layer for semiconductor deviceswhich includes depositing a layer of silicon and at least one additionalelement on the silicon substrate whereby the deposited layer issubstantially free of defects such that epitaxial silicon substantiallyfree of defects can be deposited on the deposited layer. Alternatively,a monolayer of one or more elements, preferably comprising oxygen, isabsorbed on a silicon substrate. A plurality of insulating layerssandwiched between epitaxial silicon forms a barrier composite.

Despite the existence of such approaches, further enhancements may bedesirable for using advanced semiconductor materials and processingtechniques to achieve improved performance in semiconductor devices.

SUMMARY

A semiconductor device may include a substrate and a hyper-abruptjunction region carried by the substrate. The hyper-abrupt junctionregion may include a first semiconductor layer having a firstconductivity type, a superlattice layer on the first semiconductorlayer, and a second semiconductor layer on the superlattice layer andhaving a second conductivity type different than the first conductivitytype. The superlattice may include a plurality of stacked groups oflayers, with each group of layers comprising a plurality of stacked basesemiconductor monolayers defining a base semiconductor portion, and atleast one non-semiconductor monolayer constrained within a crystallattice of adjacent base semiconductor portions. The semiconductordevice may further include a first contact coupled to the hyper-abruptjunction region, and a second contact coupled to the substrate to definea varactor.

More particularly, the hyper-abrupt junction may further include anintrinsic semiconductor layer above or below the superlattice later. Thefirst, second, and intrinsic semiconductor layers and the superlatticelayer may be parallel to underlying portions of the substrate. Thesemiconductor device may further include an intermediate semiconductorlayer between the substrate and the hyper-abrupt junction region, andthe second contact may include an implant laterally spaced apart fromthe hyper-abrupt junction region and extending from a surface of theintermediate semiconductor layer to the substrate. Moreover, thesemiconductor may further include a collector implant in theintermediate semiconductor layer below the hyper-abrupt junction region,for example. Also by way of example, the base semiconductor monolayersmay comprise silicon, germanium, etc., and the at least onenon-semiconductor monolayer may comprises at least one of oxygen,nitrogen, fluorine, carbon and carbon-oxygen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a greatly enlarged schematic cross-sectional view of asuperlattice for use in a semiconductor device in accordance with anexample embodiment.

FIG. 2 is a perspective schematic atomic diagram of a portion of thesuperlattice shown in FIG. 1.

FIG. 3 is a greatly enlarged schematic cross-sectional view of anotherembodiment of a superlattice in accordance with an example embodiment.

FIG. 4A is a graph of the calculated band structure from the gamma point(G) for both bulk silicon as in the prior art, and for the 4/1 Si/Osuperlattice as shown in FIGS. 1-2.

FIG. 4B is a graph of the calculated band structure from the Z point forboth bulk silicon as in the prior art, and for the 4/1 Si/O superlatticeas shown in FIGS. 1-2.

FIG. 40 is a graph of the calculated band structure from both the gammaand Z points for both bulk silicon as in the prior art, and for the5/1/3/1 Si/O superlattice as shown in FIG. 3.

FIG. 5 is a schematic cross-sectional diagram of a JFET including ahyper-abrupt junction incorporating superlattices in accordance with anexample embodiment.

FIG. 6 is a schematic cross-sectional diagram of an IGFET including ahyper-abrupt junction incorporating superlattices in accordance with anexample embodiment.

FIG. 7 is a schematic cross-sectional diagram of another IGFET includinga hyper-abrupt junction incorporating a single superlattice inaccordance with an example embodiment.

FIG. 8 is a schematic cross-sectional diagram of a varactor including ahyper-abrupt junction incorporating superlattices in accordance with anexample embodiment.

FIGS. 9A and 9B are schematic cross-sectional diagrams of othervaractors including a hyper-abrupt junction incorporating a singlesuperlattice in accordance with example embodiments.

FIG. 10 is a flow diagram illustrating method aspects associated withfabrication of the devices of FIGS. 5-7.

FIG. 11 is a flow diagram illustrating method aspects associated withfabrication of the devices of FIGS. 8-9.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which the example embodimentsare shown. The embodiments may, however, be implemented in manydifferent forms and should not be construed as limited to the specificexamples set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete. Like numbers referto like elements throughout, and prime and multiple prime notation areused to indicate similar elements in different embodiments.

Generally speaking, the present disclosure relates to devices having anenhanced semiconductor superlattice therein. The enhanced semiconductorsuperlattice is also referred to as an “MST” layer or “MST technology”in this disclosure and the accompanying drawings.

More particularly, the MST technology relates to advanced semiconductormaterials such as the superlattice 25 described further below. Applicanttheorizes, without wishing to be bound thereto, that certainsuperlattices as described herein reduce the effective mass of chargecarriers and that this thereby leads to higher charge carrier mobility.Effective mass is described with various definitions in the literature.As a measure of the improvement in effective mass Applicants use a“conductivity reciprocal effective mass tensor”, M_(e) ⁻¹ and M_(h) ⁻¹for electrons and holes respectively, defined as:

${M_{e,{ij}}^{- 1}( {E_{F},T} )} = \frac{{\sum\limits_{E > E_{F}}\;{\int_{B.Z.}{( {\nabla_{k}{E( {k,n} )}} )_{i}( {\nabla_{k}{E( {k,n} )}} )_{j}\frac{\partial{f( {{E( {k,n} )},E_{F},T} )}}{\partial E}d^{3}k}}}\ }{\sum\limits_{E > E_{F}}\;{\int_{B.Z.}{{f( {{E( {k,n} )},E_{F},T} )}d^{3}k}}}$for electrons and:

${M_{h,{ij}}^{- 1}( {E_{F},T} )} = \frac{{- {\sum\limits_{E < E_{F}}\;{\int_{B.Z.}{( {\nabla_{k}{E( {k,n} )}} )_{i}( {\nabla_{k}{E( {k,n} )}} )_{j}\frac{\partial{f( {{E( {k,n} )},E_{F},T} )}}{\partial E}d^{3}k}}}}\ }{\sum\limits_{E < E_{F}}\;{\int_{B.Z.}{( {1 - {f( {{E( {k,n} )},E_{F},T} )}} )d^{3}k}}}$for holes, where f is the Fermi-Dirac distribution, E_(F) is the Fermienergy, T is the temperature, E(k,n) is the energy of an electron in thestate corresponding to wave vector k and the n^(th) energy band, theindices i and j refer to Cartesian coordinates x, y and z, the integralsare taken over the Brillouin zone (B.Z.), and the summations are takenover bands with energies above and below the Fermi energy for electronsand holes respectively.

Applicant's definition of the conductivity reciprocal effective masstensor is such that a tensorial component of the conductivity of thematerial is greater for greater values of the corresponding component ofthe conductivity reciprocal effective mass tensor. Again Applicanttheorizes without wishing to be bound thereto that the superlatticesdescribed herein set the values of the conductivity reciprocal effectivemass tensor so as to enhance the conductive properties of the material,such as typically for a preferred direction of charge carrier transport.The inverse of the appropriate tensor element is referred to as theconductivity effective mass. In other words, to characterizesemiconductor material structures, the conductivity effective mass forelectrons/holes as described above and calculated in the direction ofintended carrier transport is used to distinguish improved materials.

Applicant has identified improved materials or structures for use insemiconductor devices. More specifically, Applicant has identifiedmaterials or structures having energy band structures for which theappropriate conductivity effective masses for electrons and/or holes aresubstantially less than the corresponding values for silicon. Inaddition to the enhanced mobility characteristics of these structures,they may also be formed or used in such a manner that they providepiezoelectric, pyroelectric, and/or ferroelectric properties that areadvantageous for use in a variety of different types of devices, as willbe discussed further below.

Referring now to FIGS. 1 and 2, the materials or structures are in theform of a superlattice 25 whose structure is controlled at the atomic ormolecular level and may be formed using known techniques of atomic ormolecular layer deposition. The superlattice 25 includes a plurality oflayer groups 45 a-45 n arranged in stacked relation, as perhaps bestunderstood with specific reference to the schematic cross-sectional viewof FIG. 1.

Each group of layers 45 a-45 n of the superlattice 25 illustrativelyincludes a plurality of stacked base semiconductor monolayers 46defining a respective base semiconductor portion 46 a-46 n and an energyband-modifying layer 50 thereon. The energy band-modifying layers 50 areindicated by stippling in FIG. 1 for clarity of illustration.

The energy band-modifying layer 50 illustratively includes onenon-semiconductor monolayer constrained within a crystal lattice ofadjacent base semiconductor portions. By “constrained within a crystallattice of adjacent base semiconductor portions” it is meant that atleast some semiconductor atoms from opposing base semiconductor portions46 a-46 n are chemically bound together through the non-semiconductormonolayer 50 therebetween, as seen in FIG. 2. Generally speaking, thisconfiguration is made possible by controlling the amount ofnon-semiconductor material that is deposited on semiconductor portions46 a-46 n through atomic layer deposition techniques so that not all(i.e., less than full or 100% coverage) of the available semiconductorbonding sites are populated with bonds to non-semiconductor atoms, aswill be discussed further below. Thus, as further monolayers 46 ofsemiconductor material are deposited on or over a non-semiconductormonolayer 50, the newly deposited semiconductor atoms will populate theremaining vacant bonding sites of the semiconductor atoms below thenon-semiconductor monolayer.

In other embodiments, more than one such non-semiconductor monolayer maybe possible. It should be noted that reference herein to anon-semiconductor or semiconductor monolayer means that the materialused for the monolayer would be a non-semiconductor or semiconductor ifformed in bulk. That is, a single monolayer of a material, such assilicon, may not necessarily exhibit the same properties that it wouldif formed in bulk or in a relatively thick layer, as will be appreciatedby those skilled in the art.

Applicant theorizes without wishing to be bound thereto that energyband-modifying layers 50 and adjacent base semiconductor portions 46a-46 n cause the superlattice 25 to have a lower appropriateconductivity effective mass for the charge carriers in the parallellayer direction than would otherwise be present. Considered another way,this parallel direction is orthogonal to the stacking direction. Theband modifying layers 50 may also cause the superlattice 25 to have acommon energy band structure, while also advantageously functioning asan insulator between layers or regions vertically above and below thesuperlattice.

Moreover, this superlattice structure may also advantageously act as abarrier to dopant and/or material diffusion between layers verticallyabove and below the superlattice 25. These properties may thusadvantageously allow the superlattice 25 to provide an interface forhigh-K dielectrics which not only reduces diffusion of the high-Kmaterial into the channel region, but which may also advantageouslyreduce unwanted scattering effects and improve device mobility, as willbe appreciated by those skilled in the art.

It is also theorized that semiconductor devices including thesuperlattice 25 may enjoy a higher charge carrier mobility based uponthe lower conductivity effective mass than would otherwise be present.In some embodiments, and as a result of the band engineering achieved bythe present invention, the superlattice 25 may further have asubstantially direct energy bandgap that may be particularlyadvantageous for opto-electronic devices, for example.

The superlattice 25 also illustratively includes a cap layer 52 on anupper layer group 45 n. The cap layer 52 may comprise a plurality ofbase semiconductor monolayers 46. The cap layer 52 may have between 2 to100 monolayers of the base semiconductor, and, more preferably between10 to 50 monolayers.

Each base semiconductor portion 46 a-46 n may comprise a basesemiconductor selected from the group consisting of Group IVsemiconductors, Group III-V semiconductors, and Group II-VIsemiconductors. Of course, the term Group IV semiconductors alsoincludes Group IV-IV semiconductors, as will be appreciated by thoseskilled in the art. More particularly, the base semiconductor maycomprise at least one of silicon and germanium, for example.

Each energy band-modifying layer 50 may comprise a non-semiconductorselected from the group consisting of oxygen, nitrogen, fluorine, carbonand carbon-oxygen, for example. The non-semiconductor is also desirablythermally stable through deposition of a next layer to therebyfacilitate manufacturing. In other embodiments, the non-semiconductormay be another inorganic or organic element or compound that iscompatible with the given semiconductor processing as will beappreciated by those skilled in the art. More particularly, the basesemiconductor may comprise at least one of silicon and germanium, forexample.

It should be noted that the term monolayer is meant to include a singleatomic layer and also a single molecular layer. It is also noted thatthe energy band-modifying layer 50 provided by a single monolayer isalso meant to include a monolayer wherein not all of the possible sitesare occupied (i.e., there is less than full or 100% coverage). Forexample, with particular reference to the atomic diagram of FIG. 2, a4/1 repeating structure is illustrated for silicon as the basesemiconductor material, and oxygen as the energy band-modifyingmaterial. Only half of the possible sites for oxygen are occupied in theillustrated example.

In other embodiments and/or with different materials this one-halfoccupation would not necessarily be the case as will be appreciated bythose skilled in the art. Indeed it can be seen even in this schematicdiagram, that individual atoms of oxygen in a given monolayer are notprecisely aligned along a flat plane as will also be appreciated bythose of skill in the art of atomic deposition. By way of example, apreferred occupation range is from about one-eighth to one-half of thepossible oxygen sites being full, although other numbers may be used incertain embodiments.

Silicon and oxygen are currently widely used in conventionalsemiconductor processing, and, hence, manufacturers will be readily ableto use these materials as described herein. Atomic or monolayerdeposition is also now widely used. Accordingly, semiconductor devicesincorporating the superlattice 25 in accordance with the invention maybe readily adopted and implemented, as will be appreciated by thoseskilled in the art.

It is theorized without Applicant wishing to be bound thereto that for asuperlattice, such as the Si/O superlattice, for example, that thenumber of silicon monolayers should desirably be seven or less so thatthe energy band of the superlattice is common or relatively uniformthroughout to achieve the desired advantages. The 4/1 repeatingstructure shown in FIGS. 1 and 2, for Si/O has been modeled to indicatean enhanced mobility for electrons and holes in the X direction. Forexample, the calculated conductivity effective mass for electrons(isotropic for bulk silicon) is 0.26 and for the 4/1 SiO superlattice inthe X direction it is 0.12 resulting in a ratio of 0.46. Similarly, thecalculation for holes yields values of 0.36 for bulk silicon and 0.16for the 4/1 Si/O superlattice resulting in a ratio of 0.44.

While such a directionally preferential feature may be desired incertain semiconductor devices, other devices may benefit from a moreuniform increase in mobility in any direction parallel to the groups oflayers. It may also be beneficial to have an increased mobility for bothelectrons and holes, or just one of these types of charge carriers aswill be appreciated by those skilled in the art.

The lower conductivity effective mass for the 4/1 Si/O embodiment of thesuperlattice 25 may be less than two-thirds the conductivity effectivemass than would otherwise occur, and this applies for both electrons andholes. Of course, the superlattice 25 may further comprise at least onetype of conductivity dopant therein, as will also be appreciated bythose skilled in the art.

Indeed, referring now additionally to FIG. 3, another embodiment of asuperlattice 25′ in accordance with the invention having differentproperties is now described. In this embodiment, a repeating pattern of3/1/5/1 is illustrated. More particularly, the lowest base semiconductorportion 46 a′ has three monolayers, and the second lowest basesemiconductor portion 46 b′ has five monolayers. This pattern repeatsthroughout the superlattice 25′. The energy band-modifying layers 50′may each include a single monolayer. For such a superlattice 25′including Si/O, the enhancement of charge carrier mobility isindependent of orientation in the plane of the layers. Those otherelements of FIG. 3 not specifically mentioned are similar to thosediscussed above with reference to FIG. 1 and need no further discussionherein.

In some device embodiments, all of the base semiconductor portions of asuperlattice may be a same number of monolayers thick. In otherembodiments, at least some of the base semiconductor portions may be adifferent number of monolayers thick. In still other embodiments, all ofthe base semiconductor portions may be a different number of monolayersthick.

In FIGS. 4A-4C, band structures calculated using Density FunctionalTheory (DFT) are presented. It is well known in the art that DFTunderestimates the absolute value of the bandgap. Hence all bands abovethe gap may be shifted by an appropriate “scissors correction.” Howeverthe shape of the band is known to be much more reliable. The verticalenergy axes should be interpreted in this light.

FIG. 4A shows the calculated band structure from the gamma point (G) forboth bulk silicon (represented by continuous lines) and for the 4/1 Si/Osuperlattice 25 shown in FIG. 1 (represented by dotted lines). Thedirections refer to the unit cell of the 4/1 Si/O structure and not tothe conventional unit cell of Si, although the (001) direction in thefigure does correspond to the (001) direction of the conventional unitcell of Si, and, hence, shows the expected location of the Si conductionband minimum. The (100) and (010) directions in the figure correspond tothe (110) and (−110) directions of the conventional Si unit cell. Thoseskilled in the art will appreciate that the bands of Si on the figureare folded to represent them on the appropriate reciprocal latticedirections for the 4/1 Si/O structure.

It can be seen that the conduction band minimum for the 4/1 Si/Ostructure is located at the gamma point in contrast to bulk silicon(Si), whereas the valence band minimum occurs at the edge of theBrillouin zone in the (001) direction which we refer to as the Z point.One may also note the greater curvature of the conduction band minimumfor the 4/1 Si/O structure compared to the curvature of the conductionband minimum for Si owing to the band splitting due to the perturbationintroduced by the additional oxygen layer.

FIG. 4B shows the calculated band structure from the Z point for bothbulk silicon (continuous lines) and for the 4/1 Si/O superlattice 25(dotted lines). This figure illustrates the enhanced curvature of thevalence band in the (100) direction.

FIG. 4C shows the calculated band structure from both the gamma and Zpoint for both bulk silicon (continuous lines) and for the 5/1/3/1 Si/Ostructure of the superlattice 25′ of FIG. 3 (dotted lines). Due to thesymmetry of the 5/1/3/1 Si/O structure, the calculated band structuresin the (100) and (010) directions are equivalent. Thus the conductivityeffective mass and mobility are expected to be isotropic in the planeparallel to the layers, i.e. perpendicular to the (001) stackingdirection. Note that in the 5/1/3/1 Si/O example the conduction bandminimum and the valence band maximum are both at or close to the Zpoint.

Although increased curvature is an indication of reduced effective mass,the appropriate comparison and discrimination may be made via theconductivity reciprocal effective mass tensor calculation. This leadsApplicant to further theorize that the 5/1/3/1 superlattice 25′ shouldbe substantially direct bandgap. As will be understood by those skilledin the art, the appropriate matrix element for optical transition isanother indicator of the distinction between direct and indirect bandgapbehavior.

Referring now to FIG. 5, the above described superlattice structures mayadvantageously be used to provide hyper-abrupt junctions in a variety ofdifferent semiconductor devices. In a typical hyper-abrupt orsuper-junction device, thin (e.g., 50 nm-300 nm) P and N layers aregrown adjacent to one another to form a super-junction channel. However,a problem with this configuration is that adjacent thin P and N layerswill tend to compensate one another through diffusion, and will limitthe mobility and amount of charge which may be effectively incorporatedinto the layers without degradation.

In the example embodiments presented herein, one or more diffusionblocking superlattice layers, such as the MST superlattice layersdiscussed above, are advantageously incorporated into a hyper-abruptjunction stack. The superlattice layers advantageously blockinter-diffusion, and accordingly increase the available charge withhigher mobility due to less ionized impurity scattering. In accordancewith a first example, a JFET 100 illustratively includes a semiconductorsubstrate 101 with a back gate 102 therein. Spaced-apart source anddrain regions 104, 105 with respective contacts 106, 107 are formed onthe back gate 102, and a hyper-abrupt junction region 108 is also formedon the back gate between the source and drain regions. Furthermore, backgate reach through regions 109 with contacts 110 are coupled to the backgate 102, and isolation regions 111 (e.g., an oxide) separate the backgate reach through regions from the source drain regions 104, 105. Itshould be noted that, in some embodiments, the back gate reach throughregions 109 could instead extend from a back side of the substrate 101rather than from the top/front side as shown, in which case thecontact(s) 110 would be on the back side of the substrate.

More particularly, the hyper-abrupt junction region 108 illustrativelyincludes a first semiconductor layer 112 having a first conductivitytype (N or P), a first superlattice layer 125 a on the firstsemiconductor layer, a second semiconductor layer 113 on the firstsuperlattice layer and having a second conductivity type different thanthe first conductivity type (P or N), and a second superlattice layer125 b on the second semiconductor layer. Furthermore, a gate overliesthe second superlattice layer 125 b and illustratively includes a gateelectrode 115, which will typically be the same conductivity type as theback gate 102 and the first semiconductor layer 112 (i.e., the firstconductivity type), while the semiconductor layer 113 and source/drainregions 104, 105 will be the same conductivity type (here the secondconductivity type). The second semiconductor layer 113 of thehyper-abrupt junction region 108 defines a hyper-abrupt channel of theJFET 100. The superlattice layers 125 a, 125 b effectively blockinter-diffusion and thus increase the available charge with highermobility within the channel due to less ionized impurity scattering.

Referring additionally to the flow diagram 120 of FIG. 10, beginning atBlock 121, the semiconductor layers 112, 113 and superlattices 125 a,125 b may be formed in an alternating fashion as blanket layers acrossthe substrate 101, or selectively at the desired locations on thesubstrate to form the hyper-abrupt junction region 108, at Block 122. Inthe illustrated example, the superlattices 125 a, 125 b extend into thesource and drain regions 104, 105, and into the back gate reach throughregions 109, although the superlattices may be constrained within thechannel region only in some embodiments, if desired. The gate electrodelayer 115 may then be formed over the superlattice 125 b, at Block 123,followed by a gate contact 116. The source and drain regions 106, 107may be formed by doping with the appropriate conductivity type dopant(P-type for a P channel and vice-versa), at Block 125, and the back gatereach through regions 109 may be similarly formed. Isolation regions 117are also formed to separate the source and drain contacts 106, 107 fromthe gate contact. The method of FIG. 10 illustratively concludes atBlock 126.

Turning to FIG. 6, the above-described techniques may also be used formaking other FET structures, such as an IGFET 200. The IGFET 200illustratively includes a substrate 201 and a semiconductor layer 202 onthe substrate. A hyper-abrupt junction region 208 is positioned withinthe semiconductor layer 202 and extends partially into the substrate201. The hyper-abrupt junction region 208 illustratively includes afirst semiconductor layer 212 having a first conductivity type (N or P),a first superlattice layer 225 a on the first semiconductor layer, asecond semiconductor layer 213 on the first superlattice layer andhaving a second conductivity type different than the first conductivitytype (P or N), and a second superlattice layer 225 b on the secondsemiconductor layer. Moreover, the hyper-abrupt junction region 208 isU-shaped and may be formed as a filled trench structure by depositingthe above-noted layers successively within a trench extending throughthe semiconductor layer 202 into the substrate 201.

Overlying the hyper-abrupt junction region 208 are drain extensionregions 230 and a dielectric layer 228. Furthermore, a gate electrodelayer 215 overlies the dielectric layer 228 and is surrounded by a gatedielectric layer 214. A body region 233 surrounds the gate dielectriclayer and defines a conduction channel 240 adjacent the gate dielectriclayer 232. Overlying the body region 233 is a source region 234, andoverlying the source region and gate are first and second dielectriclayers 235, 236. Furthermore, a source contact layer 237 (e.g.,semiconductor) may be formed over the top side of the device 200 (i.e.,overlying the gate structure and semiconductor layer 202), and a draincontact layer 238 (e.g., a metal layer) may be formed on the back sideof the substrate 201.

Turning now to FIG. 7, in accordance with another example embodiment ofthe IGFET 200′ the hyper-abrupt junction region 208′ illustrativelyincludes a single superlattice layer 225′. More particularly, in thisexample the hyper-abrupt junction region 208′ illustratively includes afirst semiconductor layer 212′ having a first conductivity type (N orP), the superlattice layer 225′, a second semiconductor layer 213′having a second conductivity type 213′ (P or N) opposite the firstconductivity type, and an optional intrinsic semiconductor layer 239′.The remaining components of the IGFET 200′ may be similar to thosedescribed above with respect to FIG. 6.

Turning now to FIG. 8 and the flow diagram 130 of FIG. 11, a varactor300 incorporating a hyper-abrupt junction layer 308 and associatedmethod of fabrication are now described. The varactor 300 illustrativelyincludes a substrate 301 having a cathode layer 302 and a collectorlayer 303 on the cathode layer. Beginning at Block 131, the hyper-abruptjunction region 308 may be grown on the collector layer 303 of thesubstrate 301 (Block 132). More particularly, the hyper-abrupt junctionregion 308 illustratively includes a first semiconductor layer 312having a first conductivity type (P or N), a first superlattice 325 a onthe first semiconductor layer, a second semiconductor layer 313 on thefirst superlattice layer having a second conductivity type differentthan (i.e., opposite) the first conductivity type (N or P), and a secondsuperlattice layer 325 b on the second semiconductor layer.

Furthermore, an anode region 340 and associated metal layer 341 (i.e., afirst contact) are formed on the hyper-abrupt junction region 308, atBlock 133. Furthermore, a reach through implant 342 and associated metallayer 343 (i.e., a second contact) are also formed (Block 134) tocontact the cathode layer 302 of the substrate 301 (it should be notedthat this may instead be formed as a backside contact if desired in someembodiments). The reach through implant 342 is laterally spaced apartfrom the hyper-abrupt junction 308 and extends from a surface of thecollector layer 303 to the cathode layer 302. More particularly, thereach through implant 342 may have an opposite conductivity type thanthe cathode layer 302 and collector layer 303, and the collector layerand first semiconductor layer 312 may have the same conductivity type.Furthermore, isolation regions 311 (e.g., a dielectric) may be formedaround the hyper-abrupt junction region 308 and the reach throughimplant 342. The method of FIG. 11 concludes at Block 135.

Another similar varactor 330′ is now described with reference to FIG. 9Ain which the hyper-abrupt junction 308′ illustratively includes a singlesemiconductor layer 325′. More particularly, the hyper-abrupt junction308′ illustratively includes the first semiconductor layer 312′, thesuperlattice 325′, an intrinsic semiconductor layer 339′, and a secondsemiconductor layer 340′ (which also serves as the anode region). Stillanother similar varactor 330″ is shown in FIG. 9B, in which all of thecomponents are the same as in the varactor 330′ except that theintrinsic layer 339″ is below the superlattice layer 325″ instead ofabove it. The remaining components of the varactors 330′, 330″ may besimilar to those described above with respect to FIG. 8.

Further details regarding JFET, IGFET, and varactor structures mayrespectively be found in U.S. Pat. No. 7,825,441 to Eshun et al.; U.S.Pub. No. 2007/0278565 to Tu et al.; and U.S. Pat. No. 7,183,628 toCoolbaugh et al., which are hereby incorporated herein in theirentireties by reference.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. A semiconductor device comprising: asubstrate; a hyper-abrupt junction region carried by the substrate andcomprising a first semiconductor layer having a first conductivity type,a superlattice layer on the first semiconductor layer, the superlatticecomprising a plurality of stacked groups of layers, with each group oflayers comprising a plurality of stacked base semiconductor monolayersdefining a base semiconductor portion, and at least onenon-semiconductor monolayer constrained within a crystal lattice ofadjacent base semiconductor portions, and a second semiconductor layeron the superlattice layer and having a second conductivity typedifferent than the first conductivity type; and a first contact coupledto the hyper-abrupt junction region and a second contact coupled to thesubstrate to define a varactor.
 2. The semiconductor device of claim 1wherein the hyper-abrupt junction region further comprises an intrinsicsemiconductor layer above the superlattice layer.
 3. The semiconductordevice of claim 1 wherein the hyper-abrupt junction region furthercomprises an intrinsic semiconductor layer below the superlattice layer.4. The semiconductor device of claim 1 wherein the first, second, andthe superlattice layers are parallel to underlying portions of thesubstrate.
 5. The semiconductor device of claim 1 further comprising anintermediate semiconductor layer between the substrate and thehyper-abrupt junction region; and wherein the second contact comprisesan implant laterally spaced apart from the hyper-abrupt junction regionand extending from a surface of the intermediate semiconductor layer tothe substrate.
 6. The semiconductor device of claim 5 further comprisinga collector implant in the intermediate semiconductor layer below thehyper-abrupt junction region.
 7. The semiconductor device of claim 1wherein the first and second semiconductor layers each has a thicknessin a range of 50 nm to 300 nm.
 8. The semiconductor device of claim 1wherein the base semiconductor monolayers comprise silicon monolayers.9. The semiconductor device of claim 1 wherein the at least onenon-semiconductor monolayer comprises oxygen.
 10. The semiconductordevice of claim 1 wherein the base semiconductor monolayers comprisegermanium.
 11. The semiconductor device of claim 1 wherein the at leastone non-semiconductor monolayer comprises at least one of oxygen,nitrogen, fluorine, carbon and carbon-oxygen.
 12. A semiconductor devicecomprising: a substrate; a hyper-abrupt junction region carried by thesubstrate and comprising a first semiconductor layer having a firstconductivity type, a superlattice layer on the first semiconductorlayer, the superlattice comprising a plurality of stacked groups oflayers, with each group of layers comprising a plurality of stacked basesemiconductor monolayers defining a base semiconductor portion, and atleast one non-semiconductor monolayer constrained within a crystallattice of adjacent base semiconductor portions, an intrinsicsemiconductor layer on the first superlattice layer, and a secondsemiconductor layer on the intrinsic semiconductor layer and having asecond conductivity type different than the first conductivity type, thefirst, second, and intrinsic semiconductor layers and the superlatticelayer being parallel to underlying portions of the substrate; anintermediate semiconductor layer between the substrate and thehyper-abrupt junction region; and a first contact coupled to thehyper-abrupt junction region and a second contact coupled to thesubstrate to define a varactor, the second contact comprising an implantlaterally spaced apart from the hyper-abrupt junction region andextending from a surface of the intermediate semiconductor layer to thesubstrate.
 13. The semiconductor device of claim 12 further comprising acollector implant in the intermediate semiconductor layer below thehyper-abrupt junction region.
 14. The semiconductor device of claim 12wherein the first, second, and intrinsic semiconductor layers each has athickness in a range of 50 nm to 300 nm.
 15. The semiconductor device ofclaim 12 wherein the base semiconductor monolayers comprise siliconmonolayers.
 16. The semiconductor device of claim 12 wherein the atleast one non-semiconductor monolayer comprises oxygen.
 17. Thesemiconductor device of claim 12 wherein the base semiconductormonolayers comprise germanium.
 18. The semiconductor device of claim 12wherein the at least one non-semiconductor monolayer comprises at leastone of oxygen, nitrogen, fluorine, carbon and carbon-oxygen.
 19. Asemiconductor device comprising: a substrate; a hyper-abrupt junctionregion carried by the substrate and comprising a first semiconductorlayer having a first conductivity type, a superlattice layer on thefirst semiconductor layer, the superlattice comprising a plurality ofstacked groups of layers, with each group of layers comprising aplurality of stacked base silicon monolayers defining a base siliconportion, and at least one oxygen monolayer constrained within a crystallattice of adjacent base silicon portions, an intrinsic semiconductorlayer on the first superlattice layer, and a second semiconductor layeron the intrinsic semiconductor layer and having a second conductivitytype different than the first conductivity type; and a first contactcoupled to the hyper-abrupt junction region and a second contact coupledto the substrate to define a varactor.
 20. The semiconductor device ofclaim 19 wherein the first, second, and intrinsic semiconductor layersand the superlattice layer are parallel to underlying portions of thesubstrate.
 21. The semiconductor device of claim 19 further comprisingan intermediate semiconductor layer between the substrate and thehyper-abrupt junction region; and wherein the second contact comprisesan implant laterally spaced apart from the hyper-abrupt junction regionand extending from a surface of the intermediate semiconductor layer tothe substrate.
 22. The semiconductor device of claim 21 furthercomprising a collector implant in the intermediate semiconductor layerbelow the hyper-abrupt junction region.
 23. The semiconductor device ofclaim 19 wherein the first, second, and intrinsic semiconductor layerseach has a thickness in a range of 50 nm to 300 nm.